Just a few observations about the points (no pun intended!) made above:
Likelihood of blocking Manchester bound (platform 2) at Hunts Cross is negligible, as Merseyrail only use platform 2 there in their own emergency situation, e.g. if a Merseyrail unit fails in [their own] platform 3. This is why enthusiasts' trips, such as the one run a couple of weeks ago to raise funds for Alder Hey hospital invariably try to schedule a platform 2 turnback to appeal to 'micro-track spotters'.
Yes, it's possible that a unit could fail just west of Bidston, and thus affect TfW. Equally, a TfW DMU could fail at, or just either side of Bidston (a few run to the headshunt on the Birkenhead side, to avoid occupying a platform) and thus affect Merseyrail.
Another track conflict which has not been mentioned (that I can see) is the complex layout just north of Sandhills, seen in the background of the shot below. The southbound Southport line (right) crosses the northbound Ormskirk and Kirkby line (on which the unit is travelling) at a diamond. With four trains an hour on each line in each direction (plus some ECS), careful pathing is required.
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No - Platform 2 at Ellesmere Port is not electrified. See pic below.
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Electrified Platform 3 at Southport does, (BUT ONLY VERY RARELY) get used to accommodate Northern DMUs. See below.
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This, however, was an extremely unusual circumstance. 6 October 2018. A 'Northern Strike' day led to platforms 4, 5 and 6 being occupied with empty stock. The (from memory) two-hourly skeleton service provided between Wigan and Southport was thus scheduled into platform 3. The day coincided with the 'Liverpool Giants' festival in Liverpool, hence the additional crowd-control measures on the Platform 1 / 2 island. (With grateful thanks to the guys who let me past to get this rare shot!)